Metallic iron has been produced by reducing iron oxide such as iron ores, iron pellets and other iron sources. Various such methods have been proposed so far for directly producing metallic iron from iron ores or iron oxide pellets by using reducing agents such as coal or other carbonaceous material.
These processes have been carried out in rotary hearth and linear hearth furnaces. An example of such a rotary hearth furnace is described in U.S. Pat. No. 3,443,931. An example of such a linear hearth furnace is described in US 2005/229748. Both the rotary hearth furnace and the linear hearth furnace involve making mixtures of carbonaceous material with iron ore or other iron oxide fines into balls, briquettes or other compacts, and heating them on a moving hearth furnace to reduce the iron oxide to metallic iron nuggets and slag.
A limitation of these furnaces, and the methods of operating these furnaces, in the past has been their energy efficiency. The iron oxide bearing material and associated carbonaceous material generally had to be heated in the furnace to about 1370° C. (about 2500° F.), or higher, to reduce the iron oxide and produce metallic iron material. The furnace generally required natural gas or coal to be burned to produce the heat necessary to heat the iron oxide bearing material and associated carbonaceous material to the high temperatures to reduce the iron oxide and produce a metallic iron material. Furthermore, the reduction process involved production of volatiles in the furnace that had to be removed from the furnace and secondarily combusted to avoid an environmental hazard, which added to the energy needs to perform the iron reduction. See, e.g., U.S. Pat. No. 6,390,810. What has been needed is a furnace that reduces the energy consumption needed to reduce the iron oxide bearing material such that a large part, if not all, of the energy to heat the iron oxide bearing material to the temperature necessary to cause the iron oxide to be reduced to metallic iron and slag comes from burning volatiles directly in the furnace itself and otherwise using heat generated in one part of the furnace in another part of the furnace.
A method of producing metallic iron nodules in a battery of stationary hearth furnaces is disclosed comprising the steps of:                (a) assembling a furnace housing having a stationary hearth, an inlet capable of delivering reducible material to the stationary hearth from a first side, and an outlet capable of discharging reduced iron nodules from the stationary hearth from a second side opposite the first side;        (b) assembling a heating chamber beneath the stationary hearth capable of having heated fluids circulated thereto and heating the reducible material on the stationary hearth;        (c) assembling passageways capable of circulating fluids given off by heating the reducible material positioned on the stationary hearth through ports from the furnace housing above the reducible material to the heating chamber beneath the stationary hearth;        (d) assembling burners and fluid inlet ports in the furnace housing and optionally in at least one of the passageways and heating chamber to heat the reducible material on the stationary hearth;        (e) loading reducible material and optionally an underlying hearth material onto the stationary hearth through the inlet in the first side of the furnace housing;        (f) varying the temperature within the furnace housing to dry and heat the reducible material, drive off and burn volatile material from the reducible material, and reduce at least a major portion of the reducible material to form metallic iron nodules; and        (g) discharging the metallic iron nodules and optionally related material from the stationary hearth furnace through the outlet in the second side of the furnace housing.        
The loading step may be performed by a conveying device capable of positioning the reducible material and optionally the hearth material onto the stationary hearth, and the conveying device may be capable of loading the reducible material onto the stationary hearth in a substantially singular layer. Alternately, the loading step may be performed by providing on a movable device the reducible material and optionally the hearth material, and then positioning the loaded movable device onto the stationary hearth, where the movable device may then be removed from the furnace housing leaving the reducible material, and if present the underlying hearth material, on the stationary hearth before starting step (f). In yet another alternate, the movable device may remain in the furnace housing during step (f), and the movable device being removed from the furnace housing during step (g).
The discharging step may be performed by a pushing device capable of pushing at least a majority of the reduced metallic nodules through the outlet in the second side from the stationary hearth.
The method of producing metallic iron nodules in a battery of stationary hearth furnaces may further include the step of delivering at least a portion of the volatile material from the reducible material to adjacent the burners to be capable of being burned. In addition, the heating chamber may be assembled with baffles to increase the residence time of heated fluids in the heating chamber and heat the reducible material on the stationary hearth in the furnace housing.
The method may further include steps of assembling a flue adjacent the heating chamber capable of heating fluids passing therethrough, and transferring fluids heated in the flue into the furnace housing.
Also disclosed is a battery of stationary hearth furnaces capable of producing metallic iron nodules comprising:                (a) a furnace housing having a stationary hearth, an inlet capable of delivering reducible material to the stationary hearth from a first side, and an outlet capable of discharging reduced iron nodules from the stationary hearth from a second side opposite the first side;        (b) a heating chamber beneath the stationary hearth capable of having heated fluids circulated thereto and heating reducible material on the stationary hearth;        (c) passageways capable of circulating fluids given off by heating reducible material on the stationary hearth through ports from furnace housing above the reducible material to the heating chamber beneath the stationary hearth;        (d) burners and fluid inlet ports in the furnace housing and optionally in at least one of the passageways and heating chamber capable of drying and heating the reducible material, driving off and burning volatile material from the reducible material, and reducing at least a major portion of the reducible material to form metallic iron nodules;        (e) a movable loading device capable of loading reducible material and optionally an underlying hearth material onto the stationary hearth through the inlet in the first side of the furnace housing; and        (f) a discharging device capable of discharging metallic iron nodules and optionally related material from the stationary hearth through the outlet in the second side of the furnace housing.        
The loading device may be capable of positioning the reducible material and optionally the hearth material onto the stationary hearth. The loading device may be capable of loading the reducible material onto the stationary hearth in a substantially singular layer. Alternately, the stationary hearth furnace may comprise a movable device capable of being loaded with the reducible material and optionally the hearth material, and then capable of being positioned on the stationary hearth. The movable device may be capable of being removed from the furnace housing leaving the reducible material and if present the underlying hearth material on the stationary hearth.
The discharging device may be capable of pushing at least a majority of the reduced metallic nodules from the stationary hearth through the outlet in the second side in the furnace housing. The heating chamber may have baffles to increase the residence time of the heated fluids in the heating chamber and heat the reducible material on the stationary hearth in the furnace housing. The hearth furnace may further include a flue adjacent the heating chamber and capable of receiving and heating fluids and transferring heated fluids from the flue into the furnace housing.